1. Field of the Invention
The present invention relates to a method for regenerating noble metal-containing highly siliceous zeolite hydrocarbon conversion catalysts. Such catalysts which have been deactivated during hydrocarbon conversion are regenerated by sequential contact with hydrogen, an inert gas containing 0.001 to 10 wt. % Cl in the form of HCl, an inert gas containing 0.001 to 10 wt. % Cl in the form of Cl.sub.2 or a Cl-containing organic material, and hydrogen.
2. Description of the Prior Art
The deactivation of noble metal-containing hydrocarbon conversion catalysts due to the deposition on the catalyst of carbonaceous residues is a well-known phenomenon which has received much attention in the technical and patent literature. The problem with regard to catalyst deactivation is particularly acute with respect to supported noble metal-containing catalysts employed in the reforming of naphtha feedstocks. Undesired metal migration and agglomeration can occur during preparation, calcination, or oxidative regeneration of such catalysts, resulting in significant losses in catalyst properties such as activity.
Numerous methods have been suggested by prior workers for the regeneration of supported noble metal catalysts which have been deactivated by the deposition of carbonaceous residues. In U.S. Pat. Nos. 2,916,440; 3,243,384; 3,201,355; and 3,654,182 there are disclosed procedures utilizing gaseous mixtures containing oxygen and a halogen or halogen compound, particularly hydrogen chloride, for dissipating carbonaceous residue. In U.S. Pat. No. 3,378,419 there is disclosed a procedure for the regeneration of supported platinum catalysts involving (a) addition of halogen to the catalyst while in contact with the process feedstock; and (b) burning the coke deposits from the catalyst with an oxygen-containing, halogen free regeneration gas. It is also known in the art to regenerate platinum group metal-containing zeolite catalysts. Regeneration of noble metal-loaded zeolite catalysts requires certain procedural modifications because the metal must be returned in a dispersed form within the zeolite pores. U.S. Pat. No. 3,986,982 to Crowson et al treats deactivated platinum group metal-loaded zeolites by contacting them with a stream of an inert gas containing from 0.5 to 20 percent volume of free oxygen and from 5 to 500 ppm volume of chlorine as Cl.sub.2, HCl, or an organic chlorine-containing material. The resulting catalyst is purged to remove residual oxygen and chlorine and then reduced in a stream of hydrogen at 200.degree. to 600.degree. C.
U.S. Pat. No. 4,359,400 to Landolt et al. teaches a method of regenerating deactivated supported multi-metallic platinum-containing hydrocarbon conversion catalysts in the absence of oxygen or oxygen sources. The catalysts are contacted with an oxygen-containing gas at elevated temperatures followed by contact with a dry oxygen-free, hydrogen halide. The catalyst is then activated in the presence of chlorine gas in the absence of oxygen or oxygen sources such as water, followed by reduction with hydrogen. The catalysts regenerable by Landolt et al's method may contain support materials comprising an aluminosilicate zeolite such as naturally occurring or synthetic erionite, mordenite, or faujasite.
The prior known methods notwithstanding, regeneration of highly siliceous materials which contain noble metals has been found to be particularly difficult. For example, treatment of agglomerated platinum on silica using a variety of chlorine containing compounds with water and oxygen in an inert gas results in a large loss of platinum from the silica support. Similarly, the zeolite regeneration process of U.S. Pat. No. 3,986,982 described above has not been found suitable for use in the regeneration of highly siliceous zeolites, that is, for example, zeolites having a framework silica to alumina ratio of at least about 20, say about 30.